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Abstract

Ecosystem degradation in Iceland has been severe since man arrived 1100 years
ago. Birch woodlands cover has declined from 25% of the land area, to only 1%. The
deforestation is considered to be the initial stage in the land degradation process,
followed by surface destabilization, and later erosion. The objective of this study was to
quantify and evaluate factors that contribute to the early stages of land degradation in
Icelandic ecosystems. Specific objectives were to improve our understanding of how
livestock grazing might initiate early degradation stages, elucidate field-based landscape
metrics useful for characterizing degradation stages, and to determine if landscape
metrics obtained from remote sensing data can be used to detect landscape structure
changes and identify degraded and at risk rangelands in real time over extensive and
remote areas. A State-and-Transition conceptual model was constructed for the
experimental area to identify potential key processes in the degradation sequence, and to
formalize research questions. Experimental plots were established in five plant
community types representing a space-for-time degradation sequence.
Birch seedling (Betula pubescens Ehrh.) growth and survival was reduced with
repeated clipping treatment applied to simulate browsing, but the amount of decline varied with plant community type. This suggests that continuous grazing may contribute
to deforestation, as regeneration will be reduced over time.
Intense grazing treatments, simulating both grazing and trampling, increased
surface instability and soil loss compared to grazing only or control, suggesting that
intense grazing may contribute to surface destabilization and therefore to land
degradation. Erosion appeared to be active in the most intense treatments, also within
the woodlands. The data indicate that the woodlands may have lower resilience than the
other plant communities as treatment effects appeared quicker there. The woodlands
may thus be particularly vulnerable to intense grazing.
The landscape metrics used to quantify changes in landscape surface properties
over a 51 year period yielded inconclusive results, either because of data limitations or
because of non-detectable erosion activity.
The results do generally support the proposed S&T model for the experimental
area. It is concluded that grazing may contribute to woodland decline, and intensify
degradation processes.